Selective switch



June 18, 1935. J, BOWNE SELECTIVE swITcH Filed. Feb. 6, 1954 lNl/E N TOR L. J. 80 WNE A TTORNEV Patented June 18, 1935 UNITED STATES PATENT oFFicE SELECTIVE swrron York Application February 6, 1934, Serial No. 709,943

5 Claims.

This invention relates to selective switches and particularly to those employed in automatic and semi-automatic telephone systems.

The object of the invention is to improve the operation of these switches by enabling a more positive test to discriminate between the conditions existing on the circuits being tested.

In switches of the non-numerical or line-hunting type, such as the finder switch shown in the patent to Stokely No. 1,799,654 of April 7, 1931, it has been the practice to use a single relayfor controlling the stepping action of the switch and also, for testing the condition of the circuits over which the switch brushes pass. This relay and the hunting or rotary stepping magnet have their operating circuits each dependent on the other to thus cause the stepping movement of the switch by said magnet. Since the test terminal of the line for which the switch is hunting is identified by potential of one polarity, and since other lines may present potential of the opposite polarity, each time the switch encounters one of these latter lines, a short circuit is closed around the winding of said relay, which at this time is in its operated condition. This tends to delay the release of the relay and consequently to retard the hunting speed of the switch. To avoid this, the practice has been to stiffen the adjustment on the relay springs to insure that it will release promptly under these conditions. On the other hand when the desired line is reached said relay is required to remain energized, to thus stop the switch, in series with a considerable amount of resistance. Thus the said stepping 'and test relay must be capable of releasing and holding under two sets of opposing conditions.

According to a feature of this invention an improvement is secured in these switches by introducing a space-discharge tube in the circuit of said stepping and testing relay in such a way that the unlimited resistance of the tube'prevents any fiow of current through the winding of the relay while the switch is passing over unwanted lines.

therefore, unnecessary to stiffen the adjustment of the springs. When, however, the desired line is reached, the potential encountered is of the proper polarity to cause the tube to discharge. Current now flows through the relay winding, and the relay, having a normal spring adjustment, is easily able to hold its armature attracted although there is resistance in circuit with its winding.

The foregoing and other features of the in- This eliminates any tendency to' retard the releasing action of the relay, and it is,

vention will be more readily understood from the following detailed description, which should be considered in conjunction with the accompanying drawing, and also from the appended claims.

Referring now to the drawing the single figure shows a line or trunkfinder circuit LF, a calling subscribers station S, and the calling subscribers line circuit LC. Associated with the line or trunk finder LF over leads M, 5 and l 6, and individual to the line or trunk finder, is a trunk circuit, a repeater circuit, or a selector circuit (not shown) over which an originating call is extended towards the called subscribers station. These'circuits succeeding the finder are not shown, nor will a description of theiroperation be given, since the features of this invention are confined to the operation of the finder circuit LF in its selection of a calling line or trunk. The finder circuit LF is of the well-known Strowger type, but the invention may be applied to systems using other 20 types of switches.

Associated with the circuits of the finder is a space-discharge tube 1. This tube is of the coldcathode gas-filled discharge type which breaks down and becomes conducting when certain potential conditions are applied to its electrodes.

Assuming that the subscriber at station S originates a call, the removal of his receiver from the receiver hook causes line relay 3 to operate over an obvious circuit over line 2. In operating, line relay 3 connects battery, through the winding of the'cut-off relay 4, to the sleeve conductor terminal 5 of the line finder terminals. 'The tip and ring conductors of line 2 are connected to finder terminals 6 and 7, respectively, and these terminals are associated with sleeve terminal 5 with respect to their position on the finder bank. Relay '3, in operating, closes an obvious circuit for operating group relay 8, which is common'to all of the linesiin the group with line 2. In operating, relay 8 connects ground to starting conductor 9. and also connects ground over conductor I tothe commutator segment, of all finders having access to line 2, which corresponds to the level in which the terminals of line 2 are located. Conductor I0 is shown'connected to the fourth segment of commutator H, and line 2 is therefore assumed to be connected to terminals in the fourth level of the finder bank;

Assuming that the finder LP is idle, starting relay l2 operates in a circuit from battery through its winding, inner upper back contact of delay 13, over conductor 9, to ground over the lower front contact and armature of relay 8. In operating, relay l2 connects ground over its inner upper armature and front contact to the associated trunk, repeater or selector circuit over sleeve conductor M. Relay l2 also opens the circuit to the release magnet I! over its outer upper back contact, and, in addition, closes the circuit from ground over its middle upper front contact and armature, armature and back contact of the vertical stepping magnet l8, back contact and armature of the rotary stepping magnet I9, upper winding of stepping relay 2%, to battery over the middle upper back contact and armature of relay l3, causing stepping relay 2|) to operate. The stepping relay 20, in operating, closes a circuit from ground over the middle upper front contact of relay |2, front contact of relay 2!], inner upper back contact of relay 2|, winding of the vertical stepping magnet l8, to battery over the middle upper back contact of relay i3. The vertical stepping magnet i8 opcrates and steps the shaft (not shown) and brushes 22 to 2'! inclusive up to the first group of bank terminals. The vertical off-normal springs VON are actuated as soon as the shaft is moved out of its normal position, ground being thereby connected through the lower front contact of these springs to conductor 39. In operating, magnet |8 opens the circuit through the upper winding of the stepping relay 2|). The commutator brush 28 is now in contact with the segment of. the commutator l which corresponds to the group of lines which are connected to terminals in the first level of the multiple bank. Brush 28 is connected through the lower winding of relay 2|, back contact of "the rotary stepping magnet i9, upper winding of the stepping relay 2|), to battery over the middle upper back contact of relay I3, but stepping relay 20 releases when magnet 8 operates since the lower winding of relay 2| and the upper winding of relay 2%) are not energized until the brush 28 contacts the fourth commutator segment (to which ground was connected by the operation of group relay 8). In releasing, relay 2!! opens the circuit through I the vertical stepping magnet l8, which releases and in turn closes the operating circuit for relay 29 through the upper winding of that relay.

The vertical stepping magnet l8 and the stepping relay 2!] alternately operate and release thereby elevating the line-finder shaft step by step until the commutator brush 28 contactsthe commutator segment which corresponds to the level in which the terminals of the calling line are located (in this case the fourth segment).

-When brush 28 contacts the fourthv segment,

ground over the upper front contact of relay 8, fourth commutator segment and brush 28, is connected through the lower winding of. relay 2|, over the upper back contact of the rotary stepping magnet l9, through the upper winding of relay 20, to battery over the middle'upper back contact of relay l3, causing relay 2| to operate and relay 20 to hold operated. Relay 2| locks in a circuit from battery over the middle upper back contact of relay i3, winding of vertical magnet l8, upper winding of relay 2!, upper middle front contact of relay 2|, to ground over the middleupper front contact of relay l2. The foregoing circuit is not efiective in holding the vertical stepping magnet l8 and this magnet thereforej releases. Relay 2|, in operating, opens the operating circuit through the vertical stepping magnet It and closes a circuit from battery through the winding of the rotary stepping magnet l9,

inner front contactcf relay 2| front contact of relay 2!), to ground over the middle upper front contact of relay l2. Vertical stepping magnet 8 releases and rotary stepping magnet |9 operates. In operating, magnet l9 opens the circuit through the upper winding of. relay 20 and through the lower winding of relay 2| and advances the two sets of multiple brushes (22, 24, 25 and 23, 25 and 21, respectively) to contact the first two sets of terminals in the selected level of the line or trunk finder bank. Relay 2| is of the slow-to-operate type and provides an interval between the last vertical step and the first rotary step to insure that the brushes will not be vibrating when they enter the banks thereby eliminating the possibility of the snagging of these brushes. 7

As stated hereinbefore, the characteristics of tube I are such that when certain potential conditions are applied to its electrodes the tube breaks down or ionizes and its gaseous content becomes conducting. One cathode of tube is connected through resistance 30, to the positive terminal of 48-volt battery 32. The second cathode of tube is comiected'to brush 22 in a circuit which may be traced from the left cathode, lower front contact of relay 2, inner upper back contact of relay 29, inner upper back contact of relay 3|, and through the lower Winding of relay 29. This left cathode is also capable of being connected to brush 23 in a circuit over the lower front contact of relay |2, outer upper back contact of relay |3, I

toeither of the first two sets of bank terminals,

the lines or trunks connected to these first sets of terminals are therefore either idle or busy and their associated sleeve-bank terminals (corresponding to sleeve terminals 5 and 33) present one of four conditions to the brushes 22 and 23 of the hunting finder LF. First, if connected to an idle line, no potential exists on the sleeve terminal, as, for example, no potential would be present on sleeve terminal 5 if line 2 were idle since relay 3 would not be operated to connect the battery through the winding of relay 4 to terminal 5. Second, if connected to a busy line, the sleeve bank terminal has ground connected to it after the selector, repeater or trunk circuit associated with the particular finder connected to that line has functioned. Third, if connected to a line which has just been selected by a finder and before the selector, repeater or trunk circuit associated with that particular finder has functioned to return the busy ground, as set forth in the second condition, the sleeve terminal has a potential of approximately volts negative.-

Fourth, if connected to a busy line and message registration is taking place on that line, the sleeve terminal presents a positive potential of approximately 60 volts to the sleeve brush of the hunting line-finder.

When the operation of rotary magnet l9 advances the two sets of brushes to contact the first cathode of potential, negative 10 volts or positive volts is impressed on the left cathode of tube I this time. None of these potential conditions is, however, effective in causing tube to ionize or break down, and the tube therefore remains in the non-conducting condition. As stated previously, rotary magnet 19, in operating, opens the circuit through the upper winding of relay 2i and through the lower winding of relay 2i, releasingrelay 20. In releasing, relay 2%! opens the circuit through rotary magnet l8, and the release of magnet l9 again closes the circuit through the upper winding of relay 253. The stepping relay 2!? and rotary magnet la are, therefore, alternately operated and released to advance the line or trunk finder brushes step by step until sleeve brush 22 or sleeve brush 23 makes contact with the sleeve terminal of that set of terminals to which the calling line is connected. i

If and when brush 23 makes contact with the sleeve terminal of the calling line, a circuit is closed from the negative terminal of the 48-v-olt office battery, through the winding of cut-off relay i, over the up er front contact of line relay 3, sleeve terminal 5, brush 23, lower Winding of relay 3 l, outer upper back contact of relay l3, lower front contact of relay E2, to the left cathode of tube I. With negative 48 volts on its left cathode, and positive 48 volts from battery 32 through resistance 38 on its right cathode, tube I ionizes and becomes conducting, thereby completing a circuit from the positive terminal of battery 32, through the lower Winding of relay 29, anode of tube 5, left cathode of tube 1, lower front contact of relay i2, outer upper back contact of relay 5%, lower winding of relay 3!, brush 23, sleeve terminal 5, to the negative terminal of the oflice battery through the winding of cut-off relay 4. Cut-off relay 6 operates and relay 3! is energized sufiiciently to close its inner front contact. The upper winding of relay 3! is thereby energized in a circuit from battery through its upper winding and locking contact, lower front contact of magnet l9, front contact of relay 26, to ground over the middle upper front contact of relay l2. Re lay 3i, which completely operates in the circuit through its upper winding, extends the connection through to the associated selector, repeater or trunk circuit over conductors i5 and it. The tip circuit of the line may be traced over bank terminal 6, brush 2%, outer back contact of relay 29, outer front contact of relay 3 i, and over conductor i5. The ring circuit may be traced over bank terminal l, brush 2i, neXt-to-outer back contact of relay 29, neXt-to-outer front contact of relay 3!, and over conductor l6.

Assume that the calling line does not connect to bank terminals 5, ii and i, .as'shown, but is connected instead to bank terminals 33, 3t and 35. In this instance, if and when brushes 22, 24 and 25 contact terminals 33, 34 and 35, respectively, a circuit is closed from the negative terminal of the l8-volt office battery, through the winding of cut-off relay 4, over the sleeve bank terminal 33, brush 22, through the lower winding of relay 29, inner back contact of relay 3i, back contact of make-before-break contacts of relay 29, lower make contact of relay I2, to the left cathode of tube I. Since the potential difference between its cathodes is now sufficient to cause ionization, tube I breaks down and becomes conducting, thereby completing a circuit from the positive terminal of battery 32, through thelower winding of relay 29, anode and left tube I, lower front contact of relay IE, to the negative terminal of the ls-volt ofiice battery through the lower winding of relay 29 and the winding of cut-01f relay t over a previously traced circuit. Cut-off relay d operates and relay 29 is energized sufficiently to close its inner front contact. The upper winding of relay 29 is thereby energized in a circuit from battery through its upper winding and locking contact, front contact of the make-before-break contacts of relay 2i, lower front contact of mag- A net i9, front contact of relay 25], the ground over the middle upper front contact of relay i2. Relay as, which completely operates in the circuit through its upper winding, closes a circuit for operating relay 3i. This circuit may be traced from battery through the upper winding of relay 3!, over the middle front contact of relay 2?, lower front contact of magnet l9, front contact of relay at, to ground. over the middle upper front contact of relay l2. With relays 29 and 3i both operated, the connection .from the calling line over terminals 34 and t5 and brushes 2 and respectively, is extended to conductors i5 and it and thence to the associated selector, repeater or trunk circuit.

If brush 23 finds the calling line, the complete operation of relay 36 is effective to shortcircuit its lower winding. If brush 22 finds the calling line, the complete operation 'of relay 29 is effective to short-circuit its lower winding. In either case the cut-off relay l is held operated over the particular sleeve terminal and brush, over either the next-to-inner front contact of relay 3! and back contact of the make-beforebreak' contacts of relay 2%), or over the next-toinner make contact of relay 29, and over the lower front contact of relay l2, cathode-anode circuit of tube I, and lower winding of relay 29 to the positive terminal of battery 32. The complete operation of relay M is, in either case, also effective to open the circuit through the lower winding of relay 2%, and to close a circuit for operating relay 53. This operating circuit for relay it may be traced from battery through its lower winding, over the middle armature and front contact of relay 3!, to ground over the lower armature and front contact of the VON springs. In operating, relay it closes a circuit from conductor i i, in parallel with ground over the inner upper front contact of relay 82, to brush 22 or brush 23 and to the left cathode of tube i over the lower front contact of relay i2. This ground holds the cut-off relay i operated, and also since the potential on the left cathode and also on the anode of tube l is positive, the tube is caused to deionize, thereby opening the circuit through the lower winding of relay 2b, which releases. Relay E3, in operating, also closes an additional holding circuit for relay 3l from battery through the upper winding and inner front contact of relay 39, over the lower front contact of relay [3, to ground over the inner front contact of relay l2 over conductor 3'8. The operation of relay it also opens the circuit from battery over its middle upper armature and back contact through the winding of magnet I8 and the upper winding of relay 2!. Relay 2!, in releasing, disconnects the upper winding of relay 29, if operated, from the lower armature of relay is and connects this winding to ground over the lower armature and front contact of the VON springs.

In operating, relay Iii is also effective in closing a circuit from battery through its upper winding and inner upper front contact to the starting conductor 9 and to extend this conductor over its inner upper armature, over conductor 36, to the next finder in the same group with finder LF. Relay I? also opens the circuit from ground over conductor 9 to the winding of relay I2. Relay I2 is slow in releasing so that the ground over its inner upper front contact is not disconnected from conductor 37 until after ground has been returned to this conductor by the associated selector, repeater or trunk circuit (not shown) over conductor l4. Relay l2, in releasing, opens the circuit from ground to conductor 38, opens the circuit from ground over conductor I l, outer upper front contact of relay [3, lower front contact of relay I2 to the left cathode of tube I, opens the circuit from ground to conductor 31, this conductor having previously become grounded over conductor I 4, and, in addition. connects its upper back contact in parallel with the middle front contact of relay 3!, thus rendering the circuit through the lower winding of relay 53 independent of the continued operation of relay 3|.

The aforementioned operation of cut-oif relay 4 opens the circuit through the windings of the subscribers line relay 3. The release of relay 3 opens the circuit through the winding of the group relay 8 causing relay 8 to release unless a call has been originated by a subscriber on some other line in the same group with line 2.

When the calling line is extended over conductors i5 and It, by the operation of relay 3| as hereinbefore described, the succeeding circuits function in response to impulses from the dial at station S, and the connection may be completed to the called station in a manner well known to the art.

Upon the termination of the conversation, disconnection at the calling end causes the circuits succeeding the line-finder LP to release and remove the ground from conductor M. The removal of this holding ground from conductor l4 causes the release of relays 3i and 4 when the line is connected to terminals 5, 6 and 1, as illus trated. Should the line be connected to terminals 33, 34 and 35, the removal of ground from conductor M also causes the release of relays 3| and 3. In either case, the release of relay 3! closes a circuit from ground over the lower front contact and armature of the VON springs, over the upper back contact of relay l2, outer upper back contact of relay 3i, middle back contact of relay 2 i, upper armature and front contact of the VON springs, to battery through the winding of the release magnet II. In operating, magnet l1 causes the line-finder brushes to restore to normal at which time the VON springs are returned to their normal position thereby opening the circuit through the winding of the release magnet H and opening the ground from the upper winding of relay 2e and from the lower winding of relay i3. Relay 29 releases and relay l3 also releases unless the starting conductor 53 is grounded in which case relay 83 holds operated through its upper winding until the ground is disconnected by the release of the group relay 8.

While the invention has been shown in connection with a finder switch for subscribers telephone lines, it is obviously applicable to switches of other types and for other uses.

What is claimed is:

1. In combinations. switch having a plurality. of fixed circuit terminals and a movable contact for testing the condition of said terminals, means for placing potential of either polarity on said terminals, a stepping magnet for moving said contact over said terminals, a relay for controlling the stepping action of said magnet, a spacedischarge device arranged to permit or prevent the flow of current between its electrodes according to the potential applied thereto, and means for including said device in circuit with said movable contact and said relay.

2. In combination, a switch having a contact bank and a test brush for engaging the contacts of said bank, means for placing a potential of either polarity on said contacts, a stepping magnet for advancing said test brush over the contacts of said bank, a relay for controlling the stepping action of said magnet, a gas-filled tube arranged to permit or prevent the flow of current between its electrodes according to the polarity of the potential applied thereto, and means for including said tube in circuit with said testing brush and said relay.

3. In a telephone system, a line-finder switch having a bank of fixed terminals, lines appearing in said terminals, a brush for engaging said terminals, means for placing a ground potential on said terminals to identify the lines as busy, means for placing a battery potential on said terminals for identifying the line as calling, a stepping magnet for advancing said brush from terminal to terminal, a relay for controlling the stepping action of said magnet, a space-discharge tube arranged as to permit or prevent the flow of current between its electrodes according to whether battery or ground potential is applied thereto, and means for including said tube in circuit with said brush and said relay.

4. In combnation, a switch having a plurality of fixed circuit terminals and a movable contact for testing the condition of said terminals, means for placing potential of either polarity on said terminals, a stepping magnet for moving said contact over said terminals, a discharge device having an input and two output electrodes, a circuit including one of said output electrodes, a second circuit including the other output electrode, means efiective when said movable contact engages a terminal having thereon a potential of one polarity for causing an initial flow of current in said first circuit and the subsequent flow of current in said second circuit, said discharge device being unresponsive when said contact encounters a terminal of the other polarity, and a relay in said second circuit for controlling the action of said stepping magnet.

5. In combination, a switch having a plurality of fixed circuit terminals and a movable contact for testing the condition of said terminals, means for placing potential of polarity on said terminals, a stepping magnet for moving said contact over said terminals, a discharge device having an input and two output electrodes, a circuit including one of said output electrodes, a second circuit including the other output electrode, means effective when said movable contact engages a terminal having thereon a potential of one polarity for causing an initial flow of current in said first circuit and the subsequent flow of current in said second circuit said discharge device being unresponsive when said contact encounters a terminal of another polarity, a relay having a winding controlled by said stepping magnet, and a second winding for said relay energized by current flowing in said second circuit for arresting the stepping action of said magnet.

LANGFORD J. BOWNE. 

